Electronic voltage regulator



April 23, 1946. A. F. BREWER 2,398,916

ELECTRONIC VOLTAGE REGULATOR Filed March 22, 1945 INVENTOR. ALEXANDER FREDERICK BREWER ATTORNEY Patented Apr. 23, 1946 ELECTRONIC VOLTAGE REGULATOR Alexander Frederick Brewer, Garden City, N. Y., asslgnor to Sperry Gyroscope Company, Inc., a corporation of New York Application March 22, 1945, Serial No. 584,241

2 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to electronic voltage regulators.

It is a principal object of the invention to provide an electronic regulator which is reduced in size and thus feasible for use with compact portable equipment.

For a better understanding of the invention, together with other and further object-s thereof, reference is had to the following description taken in connection with the accompanying drawing, wherein like reference characters indicate equivalent elements, and wherein:

Figs. 1-3 are schematic circuits illustrating prior circuits; and

Fig. 4 is a schematic circuit of my invention.

Fig, 1 illustrates one basic type of regulator, the degenerative type. It consists of an amplifier tube VI, a bias battery D, and the load R1 and R2. The voltage of battery D and the tap T between resistors R1 and R2 are chosen so that the control grid of the tube will never be at a positive potential with respect to the cathode.

If the input voltage in such a circuit increases by a small amount, the voltage across the load will tend to increase. Any such increase, however, will make the control grid more negative with respect to the cathode. Amplification of this grid voltage increment increases the plate cathode potential so that the load voltage change is offset. Stated mathematically:

AE,-,,=AE,,i+AE., (from the existing potential distributions) AE,, ;i AE, (from the definition of ,u)

, 1 AE AE,,= AE (from the existing po- RI+RZ tential distributions) Hence:

A vl A E07!" and in IH7 o I'AE. The stabilization factor S is given by:

Where i u=ampliilcation factor of tube VI A very desirable feature of this circuit is that the output voltage may be varied continuously by moving the tap T. Furthermore it is possible to introduce a D. C. amplifier between tap T and the control grid, thus greatly increasing the stabilization factor. Such a circuit is shown in Fig. 2. Here the static plate current of tube V2, flowing through the coupling resistor Re, furnishes grid bias for the degenerative amplifier Vi.

Fig. 3 shows several improvements that can be made in this circuit. Instead of a triode, a pentode V2 is used to obtain more gain. The cathode of V2 can be raised in potential by means of one or more gaseous voltage regulators of the VR type, so that. battery D (which will occupy more space and have more weight than its equivalent in VB tubes) can be dispensed with. Rb is a bleeder resistor for the VR tubes. And finally R1 and R: can be made independent of the load, as shown. The screen voltage of the pentode is obtained from a tap on R1 so that this voltage and consequently the mutual conductance, gm, between control grid and anode of the tube is as constant as possible.

Examining this circuit we see that if the mutual conductance of the tube at the chosen operating potentials is gm2, the voltage amplification will be approximately gmzRc, provided the plate resistance of V2 is considerably greater than Re, where 9m: is the mutual conductance of V2. The remainder of the circuit can be analyzed as follows:

as before AE AE,-' AE,(1 1) (from existing poten- R1+R1 tial distributions) Hence: AEfl|l1gm2 e o( 7)"lgin2 c and in o( 'Y) (PlgIfi c) I The stabilization factor is now:

Where:

current feedback occurs in the cathode circuit oi! V2, the VR tubes having some internal impedance. The voltage oi an amplifier with ieedback is given by the well known equation:

l-Afi where:

A=gain of amplifier without feedback s =iraction or output voltage fed back to input In this case,

i f an A=a.iR.,

I where Zr=dynamic impedance of VR tubes in cathode circuit. Hence z 010R I -Hhu b Therefore the stabilization factor of (2) is too great by the factor 1 a 1 aazt and should be written a 'Y) F lm-2 0 (3) S 1 flmz k For a 5000 volt supply, approximately thirty one, type VR 150 tubes are needed it V2 is to be a receiving type tube and y is to be made small. Assuming 07114240011. mhos at the operating point and that the Z: for each VR 150 is a resistance of 120 ohms, a value frequently obtained, the gain is reduced by the factor a 0.4, that is 60% of the available stabilization is lost. For a low voltage supply, using a single VR 105 operated so that Zs=40 ohms, resistive, and 011:2:400/1. mhos, a=.984, and the loss of stabilization due to current feedback is negligible.

A regulated high voltage supply having thirty one VR tubes is of course not small, and would be out of the question in portable or airborne equipment. The use of small neon bulbs in place of the larger VR tubes in the cathode circuit will not solve the problem as these have a much higher internal impedance than the VR tubes and, since their operating 'voltage is usually around '15 volts, a. larger number of neon tubes would be required.

In accordance with the present invention, one to six VR tubes are used to provide a reference voltage with which the varying voltage is compared. As many VR tubes as space permits should be used to make 7 small. V2 is a receiving type pentode. The plate of V2 is coupled to the grid of VI by as many neon bulbs as are needed to make the plate voltage of V2 a safe value. These bulbs may be of the watt variety which are only A" in diameter and 1" long, thus requiring very little space to obtain a large and fairly constant voltage drop. The internal impedance of these at 60 cycles is about 5000 ohms, and twenty of them used in series to obtain 1500 volts drop constitute a resistance Rn of about 100,000 ohms. Rn and Re form a voltage divider, so that the amplification or the circuit is reduced by the factor A R-+R.

In the case cited above the ain is reduced 1/1l=9% for R=1 megohm, a customary value.

The stabilization factor is now given by It may be seen then that, by using this circuit, greatly reduced size is achieved at the cost 01' somewhat reduced stabilization. The use of this scheme is best illustrated by a continuation of the above example. For a 2000 volt supply, ten VR 150 tubes would ordinarily be used. These occupy a volume oi. 62.5 cubic inches and have Z|-.=1200; 75.1; n1=4; gmz=400 4 mhos; Rc=1 meg; and Rn=0. This makes 8:970. Ii instead we use only three VR 150 tubes and nine 1 watt neons with other things the same, the following results are achieved: Rk=360; Rn=45,000; y=.'l5; 8:266, and the volume of gas tubes is 19.9 cubic inches.

While there has been described what is at present considered a preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may 1 be made therein without departing from the invention, and it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Iclaim:

1. In combination with a source of direct current power and a load circuit, a voltage regulator comprising a grid-controlled electron tube having its space-current path connected in series with said source and load circuit, and a direct current amplifier having its input controlled by the voltage across said load circuit and its output coupled to the grid of said electron tube; said amplifier comprising a second electron tube having its grid controlled by at least a portion oi the voltage across the load circuit, its cathode connected in series with a relatively low impedance gaseous discharge path to the low potential side of said load circuit, and its anode connected in series with a relatively high resistance gas discharge path and a resistor to the high potential side of said load circuit, the junction between said resistor and said discharge path being connected to the grid of said first electron tube.

2. In combination with a source 01 direct current power and a load circuit, a voltage regulator comprising a grid-controlled electron tube having its space-current path connected in series with said source and load circuit, a resistor connected across said load circuit, and a. direct current amplifier having its input controlled by the voltage across said resistor and its output coupled to the grid of said electron tube; said amplifier comprising a second grid-controlled electron tube having its grid connected to a tap on said resistor, its cathodeconnected in series with one or more gaseous, low-impedance voltage-regulator tubes to the low potential side of said resistor, and its anode being connected in series with a plurality of relatively high resistance neon tubes and a resistor, in the order named, to the high potential side of said first resistor, the Junction between the second resistor and said neon tubes being connected to the grid of said first electron tube.

ALEXANDER FREDERICK BREWER. 

